1. Technical Field of the Invention
This invention relates to a semiconductor device and method for manufacturing the same.
2. Description of the Prior Art
In order to reduce a semiconductor chip thickness, conventionally the back-surface grinding process has been carried out to grind a back surface of a semiconductor wafer after having formed devices and interconnections (hereinafter, referred to merely as a “wafer”). The back-surface grinding process has been carried out by bonding a soft protection film on a wafer surface and pressurizing the wafer via the film to urge the wafer at its back surface onto a grid stone so that the wafer is rotated in that state.
However, the wafer or chip is handled by a robot in a process after grinding, i.e. in a process to cut a wafer into chips or a process to mount the cut chip onto a leadframe. Accordingly, thickness reduction, if excessively pursued, leads to wafer or chip breakage during handling, thus resulting in yield. In particular, in the present when wafer diameter has increased, there is a fear of readily breaking a wafer having a thickness reduced by back-surface grinding.
In order to solve such a problem, there is a proposal, e.g. by JP-A-11-150090 that projection electrodes are formed on a wafer surface and thereafter a resin layer is formed on the wafer surface to use the resin layer as a protection reinforcing plate. In the manufacturing method of a semiconductor device in the laid-open publication, wafer back-surface grinding is carried out after forming a resin layer and a surface layer of the resin layer is removed by etching, thereby exposing projection electrode summits. Thereafter, the resin layer is removed along the scribe lines. Furthermore, a nitride film as a protection film is formed in an area avoiding the projection electrodes. Thereafter, the wafer is cut along the scribe lines, into individual chips.
In this method, the wafer ground at its back surface is reinforced by the resin layer and also the individual chips cut from the wafer are reinforced by the resin layer. Due to this, the wafer and chip can be handled favorably without breakage. Meanwhile, such a chip can be mounted by connecting the exposed projection electrodes onto the electrodes pads of a circuit board or the like. Accordingly, it is possible to conspicuously reduce the semiconductor device thickness as compared to the structure with connection from an external terminal by the use of a bonding wire or the like.
However, in the manufacturing method of the foregoing prior related art, there is a problem of causing a warp in a wafer due to a difference in thermal expansion/contraction ratio between the wafer and the resin layer in a course of forming a resin layer on a wafer back surface to back surface grinding, as exaggeratedly shown in FIG. 4. In case such a warped wafer is ground with a flat grid stone, the wafer after grinding has a difference in thickness at between a wafer center area and a peripheral area. Accordingly, it is impossible to obtain semiconductor chips in an even thickness. In addition, there is a fear that the semiconductor chips cut from a wafer peripheral region be not thickness-reduced to a thickness as expected.
Accordingly, it is an object of the present invention to provide a manufacturing method making it possible to overcome the above-mentioned technical problems and favorably carry out a back-surface grinding process of a semiconductor substrate by preventing a warp in the semiconductor substrate, thereby suitably manufacture a thickness-reduced semiconductor device.
Another object of the invention is to provide a semiconductor device having a structure easy to reduce the thickness.